You're over-exaggerating :) From the wiki link, the very first definition works just fine. In fact, I don't see anything about unions, disjointedness in there. Certainly, no group theory. You don't need to know how to construct, count(cardinality) or know the properties of integers(number/group theory) to know what they are for the purposes of programming. No, there's no cabal making everything more difficult than it needs to be ;D I think wiki always gets unfairly maligned for this sort of thing.